[BUGFIX][reports] Missing check for SOAP extension

Add SOAP PHP-Module to the list of required modules to be checked in the
reports module.

Change-Id: Ifad1a7e81fbec4a22707a7a12090234dbb7b9496
Resolves: #11806
Releases: 4.7, 4.6
Reviewed-on: http://review.typo3.org/6991
Reviewed-by: Steffen Gebert
Tested-by: Steffen Gebert